1. Field of the Invention
The invention relates to a fabrication method of a nitride semiconductor device comprising a nitride semiconductor (InxAlyGa1−x−yN, 0≦x, 0≦y, x+y≦1), such as a light emitting diode (LED), a laser diode (LD); light receiving devices such as a solar cell, a photosensor; or electronic devices such as a transistor, a power device; and the like.
2. Description of the Related Art
Owing to the stability in the high temperature ammonia atmosphere in its epitaxial growth process, it has been proved that sapphire is a desirable substrate for growing a light emitting device of a high efficiency made of nitride semiconductor. Practically, a nitride semiconductor device grown on a sapphire substrate is employed for a high brightness blue emitting LED, a pure green LED, and LD (laser diode) and it is applied for full color displays, signal display apparatus, image scanners, light sources such as a light source for optical disks and for media such as DVD that stores a large quantity of information, or printing apparatus. Further, applications to electronic devices such as field effect transistors (FET) are expected.
Although a nitride semiconductor is a promising semiconductor material, its bulk crystal production is difficult. For that, presently, hetero-epitaxial techniques for growing GaN by metal organic chemical vapor deposition (MOCVD) on a hetero-substrate of such as sapphire, SiC and the like are widely used. Especially, in the case of using a sapphire substrate, a method involving forming AlGaN as a buffer layer at a temperature as low as about 600° C. on a sapphire substrate and then growing a nitride semiconductor layer thereon is employed. Crystallinity of the nitride semiconductor layer is improved by such a method. Japanese Patent Application Laid-Open No. 2002-154900 discloses a structure comprising a GaxAl1−xN as a buffer layer and a crystal of a gallium nitride-based compound semiconductor grown thereon.